Photograph by J. Kauahikaua on September 27, 1997

Aerial view is from above the upper end of the southwest rift zone looking across the caldera toward the northeast. Halema`uma`u pit crater (right of center) is about 1 km in diameter and 85 m deep. Ground fractures associated with the southwest rift zone extend from Halema`uma`u through the caldera rim to bottom center of image.

Halema`uma`u emerged in the mid 1800's as a noticeable shield-shaped cone with an active lava lake at its top. This was during a time when several other vents were active on the caldera floor, and small collapses of the caldera floor were common. By 1848, observers described Halema`uma`u as being nearly as high as the lowest part of the caldera rim before subsequent collapses occurred and lava overflowed the crater. Much of the caldera floor is paved with lava flows that spilled from Halema`uma`u in 1919 and 1921.

Halema`uma`u was the principal focus of activity within the caldera from about 1838 through 1924, when the lava lake drained away and a series of steam-driven explosions and rockfalls doubled the size of the crater to about its present dimension. The collapse in 1924 lowered the crater floor to a remarkable depth of 390 m, but eruptions in the next 10 years filled the crater to a depth of 150 m.

Halema`uma`u means "house of ferns," and derives from an attempt by the legendary pig man, Kamapua`a, to hem in the volcano goddess, Pele, by building a structure made of the `ama`u fern over Pele's home.

The most recent eruptions within Halema`uma`u were in 1967-68 (251 days), 1971 (5 days), 1974 (<1 day), 1975 (<1 day), and 1982 (<1 day).